1. Field of the Invention
The present invention relates to a crank angle detecting device for a multi-cylinder internal combustion engine which is able to discriminate the operating states of the cylinders with the least possible revolution of an engine crankshaft during the starting of the engine.
2. Description of the Related Art
Conventionally, various kinds of controls on engine operations such as fuel injection control, ignition timing control, etc., are generally performed on multi-cylinder internal combustion engines by discriminating the operating states of respective cylinders in combination with crank angle. To this end, crank angle detecting devices have been widely employed.
One typical example of such a crank angle detecting device includes a crank angle sensor which generates a first signal in the form of a crank angle signal SGT representative of the crank angle of a common crankshaft, and a second signal in the form of a cylinder discrimination signal SGC used for discriminating specific operating states of the respective cylinders.
FIGS. 7(a) and 7(b) show a typical example of such signals for use with a four-cylinder internal combustion engine. FIG. 7(a) s a crank angle signal SGT which is representative of the crank angle of the common crankshaft of a four-cylinder engine. The crank angle signal SGT comprises four rectangular-shaped pulses which correspond in number to the cylinders of the engine and which are generated regularly by a crank angle sensor at predetermined crank angles (i.e., 0, 90, 180 and 270 degrees) or at predetermined angular intervals (i.e., 90 degrees). That is, the crank angle sensor generates four SGT pulses per revolution of a camshaft which is operatively connected with the crankshaft in such a manner that it makes one revolution per two crankshaft revolutions, at equally spaced angular intervals. On the other hand, FIG. 7(b) is a cylinder discrimination signals SGC which serves, in combination with the crank angle signal SGT, to discriminate respective cylinders, i.e., determine which cylinder is in a predetermined operating state or stroke. The SGC signal comprises a single rectangular-shaped pulse which has a pulse width greater than that of a SGT signal pulse and which is generated by the crank angle sensor per revolution of the camshaft (i.e., two revolutions of the crankshaft) at a timing corresponding to a predetermined operating state or stroke of a specific cylinder (e.g., the explosion stroke of a first cylinder # 1 in this example).
According to this example, discrimination of the respective cylinders is made as follows. First, an unillustrated crank angle sensor generates the SGT signal and the SGC signal which are inputted to an unillustrated control means wherein it is determined whether or not the SGC signal is at a high lever when the SGT signal is high. If it is "YES", then the control means determines that the predetermined cylinder (i.e., the first cylinder #1) is on the specified operating state (i.e., explosion stroke). Based on this determination, the respective operating states or strokes of the remaining cylinders are subsequently discriminated since the operational sequence of all the cylinders is predetermined. Accordingly, substantially one revolution (i.e., 360 degrees) of the camshaft (i.e., two revolutions of the crankshaft), is required at maximum for discriminating the operating states of the respective cylinders.
FIGS. 8(a) and 8(b) show another example of an SGT signal and an SGC signal generated by a conventional crank angle sensor for use with a four-cylinder internal combustion engine. In this example, the SGT signal is the same as that of FIG. 7(a) but the SGC signal is different from that of FIG. 7(b). Specifically, the SGC signal in this example includes two kinds of rectangular-shaped pulses within one revolution of a camshaft. One of them has a pulse width greater than that of the other, and these pulses are generated regularly by a crank angle sensor at an interval of 180 degrees or at predetermined crank angles (i.e., 0 and 180 degrees). The SGT signal and the SGC signal are inputted to an unillustrated control means wherein it is determined how many rising and falling edges of the SGT signal occurred during the time when the SGC signal is at the high level. If the number of rising and falling edges counted during the high level of the SGC is two, it is then recognized that a specific one (e.g. the first cylinder #1 in this example) of the four cylinders is on a specific operating state (e.g. explosion stroke). On the other hand, if the number counted is one, it is recognized that another specific cylinder (e.g. the fourth cylinder #4 in this example) is on a specific operating state (e.g. explosion stroke). Accordingly, based on the discriminated one of the cylinders, the respective operating states of the remaining cylinders can be subsequently discriminated in the same way as in the case of FIG. 7. Thus, substantially halt a revolution of the camshaft (360 degrees of crank angle) at maximum is required to discriminate the respective operating states of the cylinders.
In the above described conventional crank angle detecting devices, however, it is difficult to discriminate the operating states of the respective cylinders in a period of time shorter than about half a revolution of the camshaft. As a result, the conventional devices cannot meet recent demands that discrimination of the operating states of the cylinders in a multi-cylinder engine be performed in as short a time as possible, for example, within one third or fourth of one revolution or even less in order to improve engine operation such as the startability of an engine.